1. Field of the Invention
The invention generally relates to WLAN-based positioning systems and, more specifically, to methods of using devices specifically dedicated for the collection of WLAN data for use by WLAN-based positioning system to estimate a user's geographic position or optimize operation of the WLAN-enabled device or to gather more samples of WLAN signals to improve position estimates.
2. Description of Related Art
In recent years the number of mobile computing devices has increased dramatically, creating the need for more advanced mobile and wireless services. Mobile email, walkie-talkie services, multi-player gaming and call following are examples of how new applications are emerging on mobile devices. In addition, users are beginning to demand/seek applications that not only utilize their current location but also share that location information with others. Parents wish to keep track of their children, supervisors need to track the location of the company's delivery vehicles, and a business traveler looks to find the nearest pharmacy to pick up a prescription. All of these examples require the individual to know their own current location or that of someone else. To date, we all rely on asking for directions, calling someone to ask their whereabouts or having workers check-in from time to time with their position.
Location-based services are an emerging area of mobile applications that leverages the ability of new devices to calculate their current geographic position and report that to a user or to a service. Some examples of these services include local weather, traffic updates, driving directions, child trackers, buddy finders and urban concierge services. These new location sensitive devices rely on a variety of technologies that all use the same general concept. Using radio signals coming from known reference points, these devices can mathematically calculate the user's position relative to these reference points. Each of these approaches has its strengths and weaknesses based on the radio technology and the positioning algorithms they employ.
The Global Positioning System (GPS) operated by the US Government leverages dozens of orbiting satellites as reference points. Cell tower triangulation is another method used by wireless and cellular carriers to determine a user or device's location. Assisted GPS is another model that combines both GPS and cellular tower techniques to produce a more accurate and reliable location calculation for mobile users. In this model, the wireless network attempts to help GPS improve its signal reception by transmitting information about the clock offsets of the GPS satellites and the general location of the user based on the location of cell towers.
WLAN location system is a new positioning system, which uses WLAN access points to produce location of mobile users. Metro wide WLAN based positioning systems have been explored by a couple of research labs. The most important research efforts in this area have been conducted by PlaceLab (www.placelab.com, a project sponsored by Microsoft and Intel), University of California San Diego ActiveCampus project (ActiveCampus—Sustaining Educational Communities through Mobile Technology, technical report #CS2002-0714), and the MIT campus wide location system. There is only one commercial metropolitan WLAN based location system in the market at the time of this writing, and it is referred to as WLAN positioning system (WPS) herein.
FIG. 1 depicts a WLAN positioning system based on WiFi signals. The positioning system includes positioning software 103 that resides on a computing device 101. Throughout a particular target geographical area, there are fixed wireless access points 102 that transmit information using control/common channel signals. The client device monitors these transmissions. Each access point contains a unique hardware identifier known as a MAC address. The client positioning software receives transmissions from the 802.11 access points in range and calculates the geographic location of the computing device using characteristics from the radio signals. Those characteristics include the unique identifier of the 802.11 access point, known as the MAC address, Time of Arrival (TOA), and the strengths of the signal reaching the client device. The client software compares the observed 802.11 access points with those in its reference database 104 of access points, which may or may not reside on the device as well. The reference database contains the calculated geographic locations and power profile of all the access points the gathering system has collected. The power profile may be generated from a collection of readings that represent the power of the signal from various locations. Using these known locations, the client software calculates the relative position of the user device 101 and determines its geographic coordinates in the form of latitude and longitude readings. Those readings are then fed to location-based applications such as friend finders, local search web sites, fleet management systems and E911 services.
Indoor or outdoor WLAN based positioning systems have leveraged existing off-the-shelf WLAN cards without any modification other than to employ the logic to estimate position.